The present invention relates to ink jet printers and methods, and more particularly, to such methods and apparatus for shingled printing.
Ink jet printers commonly include a printhead which is mounted on a carriage assembly. The carriage assembly is moveable in a transverse direction, relative to an advance direction of a print medium such as paper. As the printhead is moved across the print medium during a particular pass of the carriage assembly, ink is selectively jetted from dot forming nozzles formed in the printhead and deposited on the print medium at corresponding ink dot placement locations in the image area of the print medium. Since the printhead moves in a direction transverse (e.g., perpendicular) to the advance direction of the print medium, each dot forming nozzle passes in a linear manner over the print medium. The line associated with each dot forming nozzle which overlies the print medium is commonly referred to as a raster or raster line. A plurality of rasters which extend across the image area of the print medium are disposed vertically adjacent to each other in the advance direction of the print medium.
Ink dot placement-related problems vary in severity with a large number of printer-related variables including desired printing speed, printhead array configurations, transfer versus direct printing, aqueous versus phase changing, required printing resolution, print post processing, if any, and the type of print medium. In particular, color ink jet printing requires careful placement of ink dots to meet current resolution and color fidelity requirements without producing undesired printing artifacts.
The field of ink jet printing is replete with references describing solutions to problems associated with placing ink dots on a print medium. In one known process, a subgroup, which is the same for all print positions of a print line, is formed from a partial number of dot forming nozzles. The dot forming nozzles of the subgroup are selectively controlled at every print position according to predetermined print data. Accordingly, depending on the print data of the respective dot forming nozzle, ink may be applied to the recording substrate. After passing across a print line, the recording substrate is advanced in accordance with the length of the subgroup in the forward feed direction. A printhead can then continue to make recordings during the subsequent return movement (bi-directional printing) or only when a new advancing movement of the printhead is effected (unidirectional printing).
If the forward feed of the recording substrate in serial printers does not correspond exactly to the respective height of the pattern which is printed line by line, adjacent print lines overlap, presenting overlaid inked areas of superimposed lines (dark stripes), or are visibly distant from one another (light stripes). These effects of incorrect line spacing are referred to in the art as line continuation errors.
Such line continuation errors are caused, for example, by manufacturing tolerances of a mechanical feed of the recording substrate. Also, the amount of feed generally varies with the thickness of the recording substrate so that costly adjustments are often needed when recording substrates with different thicknesses are employed.
One known improvement for this problem of line continuation errors is known as shingling or interlaced printing. For a 50% shingling mode (i.e., 2-pass or 50% interlace level), approximately 50% of the dots are placed on any given pass of the printhead. The candidate dots in a particular pass are selected according to a checkerboard pattern. The remaining 50% of the dots necessary to form the desired images are placed on a subsequent pass of the printhead. For a printhead with vertically disposed colors, and a raster which contains cyan, magenta and yellow dots, the printhead must be passed at least six times with a 50% shingling method, twice depositing any cyan dots present in the given raster, twice depositing any magenta dots and twice depositing any yellow dots.
While the shingling method does reduce the line continuation errors of the ink jet printing, some line continuation errors are still noticeable. Furthermore, when a shingling method is employed, the printing speed is greatly reduced. Accordingly, a printing method that further reduces the line continuation errors and maintains print speed is desired.
Accordingly, it is an object of the present invention to provide novel printing methods which overcome one or more disadvantages of the prior art. It is a more specific object of the invention to provide novel printing methods comprising an enhanced shingling method, which when employed in ink jet printing reduce line continuation errors and maintain acceptable printing speeds. It is a further object to provide apparatus for achieving such methods.
These and additional objects and advantages are provided by printing methods comprising the enhanced shingling of the present invention.
In a first embodiment, the printing methods comprise the steps of arranging a column of N dot forming nozzles for projecting ink onto a printing area comprising columns on a recording substrate, wherein N is an integer greater than 2. A scanning step is performed by moving the column of dot forming nozzles horizontally across the printing area and, in each column of the printing area, depositing one or more dots from a subgroup comprised of S dot forming nozzles from the column of N dot forming nozzles, wherein S is an integer of from 1 to about Nxe2x88x921. During the scanning step in each column of the printing area, not more than every Gth nozzle deposits a dot and a single nozzle deposits a dot not more than every Gth column, wherein G is an integer from 2 to about S. The subgroup of S dot forming nozzles is shifted vertically among the N dot forming nozzles in at least two adjacent columns according to a predetermined pattern. The recording substrate is vertically advanced in a first direction by a height of about Q nozzles, wherein Q=(S/G). The scanning step is then repeated as necessary.
In another embodiment of the present invention, the printing methods comprise the steps of arranging a column of N dot forming nozzles for projecting ink onto a printing area comprising columns on a recording substrate, wherein N is an integer greater than 2. A scanning step is performed by moving the column of dot forming nozzles horizontally across the printing area and, in each column of the printing area, depositing one or more dots from a subgroup comprised of S dot forming nozzles from a column of N dot forming nozzles, wherein S is an integer of from 1 to about Nxe2x88x921. During the scanning step in each column of the printing area, not more than every Gth nozzle deposits a dot and a single nozzle deposits a dot not more than every Gth column, wherein G is an integer from 1 to about S. The subgroup of S dot forming nozzles is shifted vertically among the N dot forming nozzles in at least two adjacent columns according to a predetermined pattern, with a provision that the predetermined pattern is not a periodic function. The recording substrate is advanced vertically in a first direction by a height of about Q nozzles wherein Q=(S/G). The scanning step is then repeated as necessary.
The printer apparatus of the present invention comprises a serial printhead, a horizontal scan drive, a vertical scan drive, and a control means. The serial printhead is comprised of a column of N dot forming nozzles for projecting ink onto a printing area comprising columns on a recording substrate, wherein N is an integer greater than 2. The control means is operative to activate the horizontal scan drive to perform and move the serial printhead horizontally across the printing area, wherein in each column of the printing area, the printhead deposits one or more dots from a subgroup comprised of S dot forming nozzles from the column of N dot forming nozzles, wherein S is an integer of from 1 to about Nxe2x88x921. During the scanning step, the control means is further operative to activate not more than every Gth nozzle to deposit a dot in each column of the printing area, to activate a single nozzle to deposit a dot not more than every Gth column, wherein G is an integer from 2 about S, and to vertically shift the subgroup of S dot forming nozzles among the N dot forming nozzles in at least two adjacent columns according to a predetermined pattern. The control means is further operative to activate the vertical scan drive to vertically advance the recording substrate by a height of about Q nozzles, wherein Q=(S/G), and then repeat the scanning step as necessary. The scanning step is then repeated as necessary.
Another embodiment of the present invention is directed to a printer apparatus comprising a serial printhead, a horizontal scan drive, a vertical scan drive and a control means. The serial printhead is comprised of a column of N dot forming nozzles for projecting ink onto a printing area comprising columns on a recording substrate, wherein N is an integer greater than 2. The control means is operative to activate the horizontal scan drive to perform a scanning step and move the serial printhead horizontally across the printing area, wherein in each column of the printing area, the printhead deposits one or more dots from a subgroup comprised of S dot forming nozzles from the column of N dot forming nozzles, wherein S is an integer of from 1 to about Nxe2x88x921. During the scanning step, the control means is operative to activate not more than every Gth nozzle to deposit a dot in each column of the printing area, to activate a single nozzle to deposit a dot not more than every Gth column, wherein G is an integer from 1 to about S, and to vertically shift the subgroup of S dot forming nozzles among the N dot forming nozzles in at least two adjacent columns according to a predetermined pattern, with the provision that the predetermined pattern is not a periodic function. The control means is further operative to vertically advance the recording substrate by a height of about Q nozzles utilizing the vertical scan drive, wherein Q=(S/G), and then repeat the scanning step as necessary.
Still other objects, advantages and novel features of the present invention will become apparent to those skilled in the art from the following detailed description, which is simply by way of illustration various modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different obvious aspects, all without departing from the invention. Accordingly, the drawings and description are illustrative in nature and not restrictive.